Toxicity assessment of Bacopa monnieri L. grown in biochar amended extremely acidic coal mine spoils

The addition of biochar in acidic mine spoils contaminated areas has been suggested for buffering and improving the fertility as well as the reduction in the metal bioavailability. This study evaluated the effect of biochar on reducing the heavy metal content in the Bacopa monnieri L. grown in the biochar amended acidic mine spoil and associated toxicological risks. The mine spoil (overburden) was treated with a biochar made from the fast pyrolysis of waste of Cymbopogon flexuosus at 450 degrees C at application rates of 15% and 20%. Plant analysis (biomass, chlorophyll, protein and lipid peroxidises), metabolite content and metal levels (Al, Cd, Cr, Cu, Fe and Pb) in the Bacopa monnieri L. herb. Hazardous quotient and acute oral toxicity of plant and its extract cultivated was carried out. The results showed that biochar amendment significantly improved biomass of the plant as well as reduced the metal content in plant tissues. The concentrations of Al, Cd, Cr, Cu, Fe and Pb in the plant tissues were within the international permissible limits. The risk assessment for bacopa consumption showed that the hazard quotients values were lower than the threshold level for herb (< 1). Application of biochar further reduced hazard quotients values the indicating safe to the consumers. In vivo toxicity also suggests that no toxic effect of bacopa extract on the albino mice. It is concluded that the application of biochar in acidic mine spoils can be not only useful for the plant growth, but also for reduction in the metal toxicity of Bacopa monnieri L., if consumed.